Ignition circuits



April 22, 1969 N. A. PARISH 3,

IGNITION CIRCUITS Filed Feb. 9. 1966 if f United States Patent US. Cl. 31527 4 Claims ABSTRACT OF THE DISCLOSURE In a spark ignition circuit a source of power is used to provide pulses of current at the secondary of a transformer, these pulses of current charging a capacitor through a diode and a spark gap so that low energy sparks are produced at the spark gap each time the capacitor is charged. The increase in charge on the capacitor serves eventually to break down a control gap, which in turn breaks down another control gap of higher break down voltage to provide a discharge path for the capacitor through the spark gap, so producing a spark of higher energy.

This invention relates to spark ignition circuits, and essentially resides in a spark ignition circuit in which sparks are produced at a spark gap, and at predetermined intervals the spark produced at the spark gap is of higher energy than the remaining sparks.

In the accompanying drawings, FIGURES l and 2 are circuit diagrams illustrating two examples of the invention, FIGURES 3 and 4 illustrate two possible forms of control gap for use in FIGURE 2, and FIGURE 5 is a circuit diagram illustrating another example.

Referring to FIGURE 1, there is provided an ignition transformer 11 having a primary winding 12 in which alternating current is produced, either by connecting the primary winding to an AC. source 13 as shown, or by connecting the primary winding to a DC. source through a mechanical or electrical interrupting circuit. The secondary winding 14 of the transformer is bridged by the anode and cathode of a diode 15 in series with a control gap 16, the control gap being bridged by a capacitor 17 and a spark gap 18 in series.

The spark gap in this example preferably has a low breakdown voltage, and could be a semi-conductor plug or a multi-gap plug.

In use, pulses of current pass through the diode 15 and charge the capacitor 17 through the spark gap 18. After a predetermined number of pulses, however, the voltage across the capacitor 17 reaches the breakdown voltage of the control gap 16, which conducts to cause the capacitor to discharge through the spark gap 18 and produce a spark of higher energy. The cycle is then repeated.

With the simple circuit shown in FIGURE 1, there is a risk that in some circumstances the control gap 16 will start to break down before the voltage across the capacitor 17 reaches the desired value so that the capacitor 17 discharges through the gap 18 at a lower energy level then required.

In order to avoid this, the circuit shown in FIGURE 2 is modified so that the secondary winding is bridged by the anode and cathode of the diode 15 in series with the capacitor 17 and spark gap 18, the spark gap being bridged by parallel circuits one of which contains a resistor 19, and the other of which contains a resistor 21 in series with a first control gap having electrodes 22, 23. A point intermediate the resistor 21 and electrode 22 is connected to the cathode of the diode 15 through a second control gap having electrodes 24, 25 and preferably the two control signors to Rotax Limited, London, England, a British gaps are contained in the same envelope as shown. The capacitor 17 charges as in FIGURE 1, producing low energy sparks at the spark gap 18, and when the voltage across the capacitor 17 reaches a predetermined value, the control gap 24, 25 breaks down, the resulting ionisation immediately causing the control gap 22, 23 which has a higher breakdown voltage, to break down rapidly. The capacitor 17 now discharges through the control gaps and the spark gap in series, the second resistor preventing the capacitor from being short-circuited through the control gap 24, 25.

The circuit shown in FIGURE 2 can' be used where the spark gap 18 has a high breakdown voltage, for example, where an ordinary air-gap plug is used. The operation is substantially the same, although it is of course necessary to adjust the circuit values.

Where two control gaps in the same envelope are used, their electrodes may be contained at opposite ends of the links of an H-shaped container 26 as shown in FIGURE 3. Alternatively, a gas filled container 27 may as shown in FIGURE 4 be provided with one electrode 22, 24 which is common to both gaps, and a further pair of electrodes 23, 25 which are spaced from the common electrode by dilferent distances.

Referring now to FIGURE 5, there are provided a pair of capacitors 31, 32 which are connected in series with diodes 33, 34 respectively across the secondary windings 35, 36 of a pair of transformers 37, 38 the primary windings 39, 40 of which may be connected to a common supply or to separate A.C. sources 41, 42 or interrupted D.C. sources. The capacitor 31 is bridged by a control gap 43 in series with a spark gap 44, whilst the capacitor 32 is bridged by a control gap 45 and an inductor 46 in series with the gap 44. The capacitors 31, 32 are charged at the same rate, but the gap 43 has a lower breakdown voltage than the gap 45. Each time the control gap 43 breaks down, a spark is produced at the spark gap 44, and after a number of low energy sparks have been produced, the charge on the capacitor 32 will have risen sufficiently to break down the control gap 45, so that a higher energy spark will be produced. The inductor 46 is not essential, but is preferably included to prevent one capacitor from discharging into the other capacitor when both control gaps are conducting. Switch means (not shown) may be incorporated to ensure that after the spark of higher energy has been produced, no sparks of lower energy are produced for a predetermined period of time. Whereafter a plurality of low energy sparks are produced, followed by another high energy spark and a further delay and so forth.

The capacitors 31, 32 could be charged from the same source, and the spark gap 44 can be an ordinary spark gap, or a multi-gap plug.

A variation of this example is a common spark gap which may be of the type containing one common electrode which is earthed, one main electrode for connection to the control gap 45 through the inductor 46, and one auxiliary electrode for connection to the control gap 43.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. A spark ignition circuit in which sparks are produced at a spark gap and at predetermined intervals the spark produced at the spark gap is of higher energy than the remaining sparks, said spark ignition circuit comprising in combination a pair of terminals, means for supplying pulses of current to said pair of terminals at predetermined intervals, a circuit connected across said pair of terminals and including in series a diode, a capacitor and said spark gap, each pulse of current applied to said terminals charging said capacitor through said diode and said spark gap and producing a low energy spark at said spark gap, first and second control gaps each having a first plate and a second plate, a resistor and second control gaps to one side of said capacitor, a connection between the second plate of the first gap and the other side of said capacitor, and a connection between the second plate of the second control gap and the side of said spark gap remote from said capacitor, said second control gap having a higher breakdown voltage than said first control gap, and said first control gap breaking down when the voltage across said capacitor reaches a predetermined value, and serving when it breaks down to break down said second control gap, whereupon said capacitor discharges through the series circuit including the spark gap, the second plate of the second control gap, the first plate of the second control gap, the first plate of the first control gap and the second plate of the first control gap.

2. A spark ignition circuit as claimed in claim 1, in which the first and second control gaps are housed in a common envelope, the remaining components of the circuit being outside the common envelope.

3. A circuit as claimed in claim 2, in which said common envelope is H-shaped with the first and second plates of the first control gap in one of the longer limbs of the H and the first and second plates of the second control gap in the other longer limb of the H.

4. A circuit as claimed in claim 2 in which the first plate of the first control gap and the first plate of the seccoupling the first plates of the first ondvcontrol gap are constituted by a common plate, the

References Cited UNITED STATES PATENTS 2,175,900 10/1939 Knight 315-206 X 2,476,773 7/ 1949 Schreiber 315-239 X 2,834,917 5/1958 Moignet 315-173 X 2,889,480 6/1959 Soulary et al 3l517l X 2,938,147 5/1960 Rose 315- 3,030,548 4/1962 Johnston 3l5-239 X 3,052,817 9/1962 Branker 3l5-17l 3,213,258 10/1965 Ferguson.

3,267,329 8/1966 Segall 315183 3,376,470 4/1968 Stone et a1 3l5173 X FOREIGN PATENTS 929,070 6/ 1963 Great Britain.

JOHN W. HUCKERT, Primary Examiner. J. R. SHEWMAKER, Assistant Examiner.-

U.S. Cl. X.R. 315l71, 173, 174, 207, 208, 209, 227, 241, 269, 276 

